Dopamine CRI from a 400 mg / 250 mL bag
A 55 lb dog has an intraoperative MAP of 55 mmHg despite fluid loading. You've prepared a dopamine bag: 400 mg of dopamine in 250 mL of NaCl. What pump rate (mL/hr) delivers 5 µg/kg/min?
Hint
Three unit mismatches to fix: lb vs kg, mg vs µg in the bag, and min vs hr for the dose. Convert weight first, then untangle the drug-amount units before doing any arithmetic.
Another hint
(1) lb → kg via 2.2 lb/kg. (2) Bag concentration: 400 mg ÷ 250 mL = 1,600 µg/mL once you put it in matching units. (3) Pump rate (mL/hr) = (dose × weight × 60) ÷ bag concentration. The 60 converts µg/min to µg/hr.
Show worked answer
-
Convert the patient's weight from lb to kg.
$$\frac{55 \,\cancel{lb}}{2.2 \,\cancel{lb}/kg} = 25 \,kg$$ -
Next, find the bag's final concentration in µg/mL. 400 mg = 400,000 µg.
$$\frac{400{,}000 \,\mu g}{250 \,mL} = 1{,}600 \,\tfrac{\mu g}{mL}$$ -
Compute the µg per minute the patient needs: dose × weight. kg cancels.
$$5 \,\tfrac{\mu g}{\cancel{kg}\cdot min} \times 25\,\cancel{kg} = 125 \,\tfrac{\mu g}{min}$$ -
Convert µg/min to µg/hr by multiplying by 60 min/hr.
$$125 \,\tfrac{\mu g}{\cancel{min}} \times 60\,\tfrac{\cancel{min}}{hr} = 7{,}500 \,\tfrac{\mu g}{hr}$$ -
Divide by the bag concentration to convert µg/hr to mL/hr. µg cancels.
$$\frac{7{,}500 \,\cancel{\mu g}/hr}{1{,}600 \,\cancel{\mu g}/mL} \approx 4.7 \,\tfrac{mL}{hr}$$ -
Titrate to a MAP of at least 65 mmHg; that's the conventional perfusion threshold below which organ blood flow becomes pressure-dependent. Below 50–60 mmHg renal autoregulation is lost and AKI risk rises sharply.
Run the dopamine bag at ≈ 4.7 mL/hr to deliver 5 µg/kg/min.